For changing gear in an automatic transmission a certain delay time is allowed for before the switching is completed. During this, the engine speed increases until the load is taken up by the coupling being engaged from the coupling being disengaged. The reasons for the delay time are clutch filling times and ramp times until the switching pressure required for the change has been built up.
In vehicles with powerful engines the engine speed difference that occurs, having regard to the clutch filling times including the load take-up, can be as much as about 1200 r/min.
The maximum attainable engine speed in kick-down upshift gear changes can therefore assume various values which are affected by the load condition of the vehicle and the road inclination.
The problem arises that in an unladen vehicle moving downhill, kick-down (KD) upshifts take place in the range of the engine cut-off speed, i.e. the maximum permissible engine speed. The reason for this is the negative driving resistance, by which the vehicle is additionally accelerated.
In such a case the kick-down upshift must take place and adjusted earlier, i.e. at lower output speed. In the loaded condition and driving uphill, in contrast, the KD switching speed is lower as a result.
Accordingly, the optimum condition, namely equal KD switching speed for any kick-down upshift, cannot be achieved.
In the prior art kick-down shifts are triggered when predetermined output speeds are exceeded. These output speed thresholds can be stored in switching programs or be defined as discrete parameters.
The purpose of the present invention, starting from the aforesaid prior art, is therefore to provide a method for kick-down switching speed optimization in a motor vehicle with an automatic transmission, such that in kick-down upshifts the engine is prevented from exceeding the maximum permissible speed. In addition, premature upshifting is to be prevented.